Field of the Invention
The present invention relates to a communication system such as LTE-A, and in particular to a PDCP operation when a user equipment has a dual connection, i.e., is connected to different base stations of a communication network, which serve different radio bearers.
Related Background Art
The following meanings for the abbreviations used in this specification apply:    CA carrier aggregation    CN core network    CP control plane    eNB evolved NodeB    EPS evolved packet system    GPRS general packet radio service    GTP GPRS tunneling protocol    GW gateway    HO hand over    IP internet protocol    L1L2 layer 1 layer 2    LCH logical channel    LCP logical channel prioritization    LTE long term evolution    LTE-A LTE advanced    MAC medium access control    RAN radio access network    RLC radio link control    RRC radio resource control    S serving    SRB signaling resource block    PDCP packet data convergence protocol    PHY physical layer    UDP user datagram protocol    UE user equipment    UP user plane    Uu air interface between UE and eNB    X2 interface between eNBs
A dual connection comprises e.g. dual connectivity of a UE to both macro eNB and pico eNB of a communication network. In addition, inter-site CA introduces the possibility of carrier aggregation between different eNBs, which also requires dual connectivity to multiple eNBs from UE point of view.
FIG. 1 shows a dual connection of a UE to a macro eNB serving a radio bearer F1 in a macro cell 1, and to a pico eNB serving a radio bearer F2 in a pico cell 2. The pico eNB and the macro eNB may communicate over an X2 interface. PDCP for different EPS bearers could be terminated differently at macro eNB or pico eNB.
FIG. 1 shows further pico eNBs of pico cells in the macro cell 1, to which the UE may hand over, which is indicated by the dashed line in FIG. 1.
A handover or RRC reconfiguration of the UE may occur from one pico eNB to another while the UE is still connected to the macro eNB. However, current PDCP operation (no PDCP reset for RRC reconfiguration or full PDCP reset for Handover) is not efficient for this event.